Method for making light alloy components

ABSTRACT

The invention concerns a method for making alloy components characterised in that after casting the preform ( 2 ) and before transferring it into a forging matrix ( 5 ), said preform, still hot at the end of casting, is transferred and completely immersed in a vessel ( 3 ) for graphitization coating, then, on coming out of the vessel, the preform temperature enabling the water to be evaporated so that the preform is homogeneously coated with graphite.

[0001] The invention relates to the technical sector of the productionof light alloy components, particularly aluminium, obtained fromcasting, forging and similar methods.

[0002] A specific method called “COBAPRESS” is disclosed in Europeanpatent EP 119,365 that combines casting and forging techniques ofaluminium or aluminium alloy components.

[0003] As a reminder, the method in question consists in castingaluminium or aluminium alloy in a mould and, after the castingoperation, in stripping the component (called a preform) while still hotat between approximately 400° C. and 500° C., of positioning thecomponent between two dies or sections of a die that define animpression the measurements of which are slightly smaller than those ofthe mould and are those of the end component, the two shells or diesections being then pressed tightly together to exert a combined effectof core pressing and superficial hammering on the cast preformpositioned between the sections of the dies.

[0004] An improved method of the type mentioned above is disclosed inFrench patent FR 2,778,125 the purpose of which is to use the preheatingoperation in order to perform the thermal treatment operationsimultaneously thereby saving on the standard thermal treatmentoperation which usually follows the heading operation. Between thecasting of the preform and the forging operation said cast preform istransferred to a furnace where the solution heat treatment of said castpreform is carried out at the solution heat treatment temperature of thematerial in which the component is produced. The component is thenpositioned between the two sections of the heading die for the forgingoperation with ambient, accelerated or hardening cooling.

[0005] The improved method called COBAPRESS 2 therefore considerablyreduces the production time and cost while achieving the samecharacteristics of the components as the COBAPRESS method disclosed inEuropean patent EP 119,365.

[0006] As standard in the forging sector, implementation of the twoversions of the method described above requires the forging die to besprayed with a solution of water plus liquid graphite in order tofacilitate the creeping of the forged metal and the stripping of the endcomponent.

[0007] In practice, spraying the forging die with a graphite solution isan operation which, depending on the complexity, of the rough endcomponent, is relatively long and expensive and does not always enablethe less accessible sections of the component to be sprayed uniformly;finally, it dirties the work station considerably.

[0008] American U.S. Pat. No. 4,683,742 is also known and disclosespreheating the billets before they are coated with a graphite or similarcoating. The billets are then forged are being sent through a dryinginstallation.

[0009] The purpose of the invention is therefore to optimise the initialCOBAPRESS method for cast-forged light alloy.

[0010] Japanese patent JP 6,005,433 is also known which describesforging billets using a graphite coating.

[0011] Regarding all the above-mentioned prior art, the applicant hasattempted to optimise the COBAPRESS method as defined in the previouspatents referred to above.

[0012] The initial approach focused on improving the conditions underwhich the graphite is deposited in the forging die by spraying agraphite solution on the forging die using robots to achieve improvedcontrol of the distribution. In practical terms this solution is lessthan satisfactory as it nevertheless requires human participation andthe same costs and environmental issues are still present.

[0013] The applicant therefore focused unexpectedly on anotherpossibility available between the two main casting and forging phases.The approach in question ensures the graphite solution is distributeduniformly on the preform and, moreover, provides characteristics whichare particularly advantageous by improving the productivity of themethod.

[0014] According to a first aspect, the method for producing light alloycomponents is of the type which implements the following phases:

[0015] casting the preform at between approximately 250° C. and 500° C.,

[0016] transferring the heated preform to a die that defines animpression the measurements of which are slightly smaller than those ofthe mould, the two sections of the die being then pressed together toexert the forging and die-stamping effect on the rough end component,

[0017] cooling the rough component at ambient temperature, the methodbeing characterised in that after casting the heated preform and beforetransferring it to a forging die said preform, which is at the end ofcasting temperature, is transferred and totally submerged in a graphitecoating tank to enable the graphite solution to be deposited on thepreform, then when the preform is removed from the tank the temperatureof the preform enables the water to evaporate naturally such that thepreform is coated uniformly with graphite.

[0018] There is therefore no further need to reheat the component forthe resistance of the coating product or to provide a system toevaporate the water as this occurs naturally.

[0019] According to another aspect, the improved method for making lightalloy components is of the type which implements the following phases:

[0020] casting the preform at between approximately 250° C. and 500° C.;

[0021] transferring the cast preform obtained to a furnace where thesolution heat treatment of said cast preform is carried out at thesolution heat treatment temperature of the material in which thecomponent is produced;

[0022] when the preform, which has been subjected to the solution heattreatment, is removed from the furnace, transferring it to a die thatdefines an impression the measurements of which are slightly smallerthan those of the mould, the sections of the die being then pressedtogether to exert the forging and die-stamping effect on the rough endcomponent;

[0023] ambient temperature, accelerated or hardening cooling of thecomponent obtained, the method being characterised in that after castingthe heated preform and before transferring it to the tunnel furnace saidpreform, which is at the end of casting temperature, is transferred andtotally submerged in a graphite coating tank to enable the graphitesolution to be deposited on the preform, then when the preform isremoved from the tank at this stage the temperature of the preform andthat of the previous phases enables the water to evaporate naturallysuch that the preform is coated uniformly with graphite, said preformbeing then returned to a temperature in the tunnel furnace thathomogenises the temperature of the graphite-coated preform.

[0024] These and other aspects will become apparent from the followingdescription.

[0025] The object of the present invention is described, merely by wayof example, in the accompanying drawings in which FIG. 1 shows theimplementation of the method of the invention.

[0026] The method for producing light alloy components of the inventionrequires an installation with five successive specific zones that coverthe various stages of the method.

[0027] First zone (Z1) is where the light alloy is cast in a mould (1)enabling a preform (2) to be obtained under the temperature conditionsdescribed above.

[0028] Second zone (Z2) is where heated preform (2) is transferred intoa tank (3) to be immersed and undergo graphite coating. The bath is agraphite and water solution.

[0029] Adjacent to the tank used for graphite coating or in the planeabove the tank a drying phase (Z3) is provided for the preformedcomponent outside the bath.

[0030] The following zone (Z4) is where the dried graphite-coatedpreform is transferred into tunnel furnace (4) to be subjected totemperature homogenisation. The following zone (Z5) is where the preformleaves the tunnel furnace to be forged in a die (5) which is rapidlylubricated using minimum lubrication limited to the land according tothe conditions specified above before being subjected to ambienttemperature, accelerated or hardening cooling.

[0031] The optimised method of the invention provides components thustreated with specific advantages.

[0032] There are many advantages to the optimised method of theinvention.

[0033] Advantage is taken of the preform temperature to enable thegraphite to adhere to the preform and then the water to evaporate beforethe subsequent operations.

[0034] a finer surface quality of the component due to the graphitesolution which is deposited uniformly and which has an effect on thebreakage test conditions;

[0035] improved resistance in fatigue tests;

[0036] increased service life of the heading tooling;

[0037] improved working environment;

[0038] increased productivity;

[0039] reduced and less complex human training, an important aspect interms of skilled labour recruitment, which is always difficult, orsimpler automation;

[0040] when the temperature of the component is homogenised in thetunnel furnace the black from the graphite bath improves calorie storageand therefore improves the structural and mechanical characteristics ofthe component;

[0041] furthermore, a shade of colour could meet appearance and colourrequirements. A subtler shade could be used for safety and particularlysuspension-chassis components to prevent them from shining under thebodywork and distracting the drivers near the vehicle in question.

[0042] There are therefore many advantages. The method is optimisedaccording to the invention and provides unexpected and recentimprovements that justify its development.

1. Method for producing light alloy components of the type whichimplements the following phases: casting the preform at betweenapproximately 250° C. and 500° C., transferring the preform to a diethat defines an impression the measurements of which are slightlysmaller than those of the mould, the two sections of the forging diebeing then pressed together to exert the forging and die-stamping effecton the rough end component; cooling the rough component at ambienttemperature, the method being characterised in that after casting theheated preform and before transferring it to a forging die said preform,which is at the end of casting temperature, is transferred and totallysubmerged in a graphite coating tank to enable the graphite solution tobe deposited on the preform, then when the preform is removed from thetank the temperature of the preform enables the water to evaporatenaturally such that the preform is coated uniformly with graphite. 2.Improved method for making light alloy components of the type whichimplements the following phases: casting the preform at betweenapproximately 250° C. and 500° C.; transferring the cast preformobtained to a furnace where the solution heat treatment of said castpreform is carried out at the solution heat treatment temperature of thematerial in which the component is produced; when the preform, which hasbeen subjected to the solution heat treatment, is removed from thefurnace, transferring it to a die that defines an impression themeasurements of which are slightly smaller than those of the mould, thetwo sections of the die being then pressed together to exert the forgingand die-stamping effect on the rough end component; ambient temperature,accelerated or hardening cooling of the component obtained, the methodbeing characterised in that after casting the heated preform and beforetransferring it to the furnace said preform, which is at the end ofcasting temperature, is transferred and totally submerged in a graphitecoating tank to enable the graphite solution to be deposited on thepreform, then when the preform is removed from the tank the temperatureof the preform and that of the previous phase enables the water toevaporate naturally, it is dried such that the preform is coateduniformly with graphite, said preform being transferred to the furnacewhere the solution heat treatment is performed on the graphite-coatedpreform.
 3. Method as claimed in either of claims 1 and 2, characterisedin that a shade of colour is introduced into the graphite coating bath.4. Installation to implement the method of any of claims 1 to 3,characterised in that it comprises the following 5 successive zones: afirst zone (Z1) where the light alloy is cast in a mould (1) enabling apreform (2) to be obtained; a second zone (Z2) where preform (2) istransferred into a tank (3) to be immersed and undergo graphite coating;a drying phase (Z3) of preformed component (2) outside the graphite bathin tank (3); a fourth zone (Z4) where the dried preform is transferredinto a tunnel furnace (4) to be subjected to temperature homogenisation;a fifth zone (Z5) where the preform leaves tunnel furnace (4) to beforged in a die (5) before being subjected to ambient temperature,accelerated or hardening cooling.